The present invention relates to a polishing apparatus and a polishing method in which a metal film surface formed on a semiconductor substrate is polished by a chemical mechanical approach.
A planarizaion process of a wafer (semiconductor substrate) in a manufacturing process is important to attain a higher integration of a semiconductor device. A CMP (Chemical Mechanical Polishing) apparatus is widely used as an apparatus planarizing a wafer. In a CMP apparatus, for example, while polishing slurry is supplied to a wafer to be polished, a metal film and the like on the wafer are polished by contact with a polishing pad.
Now, in order to selectively polish protruding portions (improve flatness) of an insulating film, a metal film and the like on a wafer, deformation of a polishing pad surface needs to be suppressed and a high hardness of the polishing pad is required. On the other hand, in order to perform uniform polishing on the entire semiconductor wafer (improve uniformity), flexibility sufficient to conform warp of the wafer is required for the polishing pad. Therefore, since there is a trade-off between flatness and uniformity in selecting a polishing pad, it is difficult to ensure both flatness and uniformity of polishing. Thus, for the purpose of improving both flatness and uniformity of the wafer, such a polishing pad is employed that has a two-layer structure formed with a hard material arranged in an upper layer in contact with the wafer to be polished and a soft material arranged in a lower layer thereof.
A wafer holding (fixing) method will now be described. Generally, in a CMP apparatus, a wafer is held using a vacuum chuck (vacuum suction), a backing film (backing pad) and the like. Advantages of using a vacuum chuck include: easiness of wafer replacement (attachment and removal); secure and firm holding of wafer; and elimination of wafer warp. As a disadvantage, the use of the aforementioned polishing pad having the two-layer structure described above cannot accommodate macroscopic thickness variations of the wafer, resulting in a poor polishing uniformity.
On the other hand, although the use of a backing pad is inferior in easiness of wafer attachment and removal and secure holding of wafer, it has an advantage in that wafer warp, thickness variations and the like can be accommodated (reduced) to some extent as the backing pad itself has a good elasticity. As a result, macroscopic undulations of the wafer can be reduced to some extent and poorer polishing uniformity can be prevented to some extent. Therefore, holding a wafer using a backing pad is presently common. A polishing apparatus using a backing pad as wafer holding means and using a polishing pad having the aforementioned two-layer structure (hard material and soft material) is disclosed for example in Japanese Patent Laying-Open Nos. 10-138123, 9-321001, 9-260318, 7-266219 and 7-297195.
The present situation of the conventional polishing method has been described above. In conclusion, the conventional CMP apparatus cannot improve both flatness and uniformity in a wafer sufficiently. This problem is outstanding particularly in case of polishing a damascene structure.
The present invention is made in view of the situation described above. A first object of the present invention is to provide a chemical mechanical polishing apparatus capable of sufficiently improving both flatness and uniformity of polishing even with a vacuum chuck excellent in easiness of wafer attachment and removal and secure holding of a wafer.
A second object of the present invention is to provide a damascene interconnection forming apparatus and method in which an accurate damascene interconnection can be formed by using a polishing apparatus realizing good flatness and uniformity.
In order to achieve the above objects, a chemical mechanical polishing apparatus in accordance with the present invention is applied to an apparatus including: a substrate holding table holding a semiconductor substrate by vacuum suction; a polishing pad being in contact with the semiconductor substrate; a platen holding the polishing pad; and an elastic member arranged between the polishing pad and the platen. It is characterized in that a material having a hardness defined by JIS standard K6301 (A type) of 10-40 and a thickness of 5-30 mm is used as the elastic member.
A damascene interconnection forming apparatus in accordance with the present invention is applied to a damascene interconnection forming apparatus forming an insulating film on a semiconductor substrate, forming a recessed portion in a prescribed region of the insulating film, forming a barrier metal film on a surface of the insulating film including the recessed portion, and forming a metal interconnection film on the barrier metal film to completely fill in at least the recessed portion, followed by polishing the metal film and the barrier metal film until the insulating film is exposed in a region other than the recessed portion. It is characterized by including: first polishing means for performing a first polishing step of polishing the metal interconnection film until the barrier metal film is exposed in the region other than the recessed portion; and second polishing means for performing a second polishing step of polishing the barrier metal film until the insulating film is exposed in the region other than the recessed portion. Furthermore, the first polishing means includes: a substrate holding table holding the semiconductor substrate by vacuum suction; a polishing pad being in contact with the semiconductor substrate; a platen holding the polishing pad; and an elastic member arranged between the polishing pad and the platen and having a hardness defined by JIS standard K6301 (A type) of 10-40 and a thickness of 5-30 mm. In addition, the second polishing means includes: a substrate holding table holding the semiconductor substrate by vacuum suction; a polishing pad being in contact with the semiconductor substrate; a platen holding the polishing pad; and an elastic member arranged between the polishing pad and the platen and having a hardness defined by JIS standard K6301 (A type) of at least 50.
A damascene interconnection forming method in accordance with the present invention is applied to a damascene interconnection forming method of forming an insulating film on a semiconductor substrate, forming a recessed portion in a prescribed region of the insulating film, forming a barrier metal film on a surface of the insulating film including the recessed portion, and forming a metal interconnection film on the barrier metal film to completely fill in at least the recessed portion, followed by polishing the metal film and the barrier metal film until the insulating film is exposed in a region other than the recessed portion. It is characterized by including: a first polishing step of polishing the metal interconnection film until the barrier metal film is exposed in the region other than the recessed portion using first polishing means; and a second polishing step of polishing the barrier metal film until the insulating film is exposed in the region other than the recessed portion using second polishing means. Furthermore, the first polishing means includes: a substrate holding table holding the semiconductor substrate by vacuum suction; a polishing pad being in contact with the semiconductor substrate; a platen holding the polishing pad; and an elastic member arranged between the polishing pad and the platen and having a hardness defined by JIS standard K6301 (A type) of 10-40 and a thickness of 5-30 mm. In addition, the second polishing means includes: a substrate holding table holding the semiconductor substrate by vacuum suction; a polishing pad being in contact with the semiconductor substrate; a platen holding the polishing pad; and an elastic member arranged between the polishing pad and the platen and having a hardness defined by JIS standard K6301 (A type) of at least 50.
In the damascene interconnection forming apparatus and method described above, preferably, the first polishing means and the second polishing means are implemented by a single chemical mechanical polishing apparatus. More specifically, the polishing apparatus includes: a substrate holding table holding the semiconductor substrate by vacuum suction; first and second platens arranged in positions opposing the substrate holding table in a polishing operation; a first polishing pad arranged on the first platen; a second polishing pad arranged on the second platen; a first elastic member arranged between the first platen and the first polishing pad and having a hardness defined by JIS standard K6301 (A type) of 10-40 and a thickness of 5-30 mm; and a second elastic member arranged between the second platen and the second polishing pad and having a hardness defined by JIS standard K6301 (A type) of at least 50. In performing the first polishing step, the substrate holding table is arranged in a position opposing the first platen, and in performing the second polishing step, the substrate holding table is arranged in a position opposing the second platen.